The present disclosure relates to subject matter contained in Japanese Patent Application No. 9-231892 (filed on Aug. 28, 1997), which is expressly incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a wire loop type instrument for an endoscope that has a wire loop at an end thereof.
2. Description of the Prior Art
Wire loop type instruments for endoscopes, such as a high-frequency snare and a basket type grasping instrument, have elastic wires expanded in a loop shape under free conditions. When withdrawn into the distal end of a sheath, the elastic wires are folded. When projecting from the distal end of the sheath, the elastic wires expand in the loop shape by their own elasticity.
Such a wire loop type instrument for an endoscope is generally arranged as shown in FIG. 9. A plurality of elastic wires 1 are bundled together at both the distal and proximal ends and inserted into binding pipes 2 and 5, respectively, in which the elastic wires 1 are fixed together.
A control wire 6 is axially movably inserted in a sheath 7. The distal end of the control wire 6 is firmly connected to the proximal end binding pipe 5, which fixedly binds together the proximal ends of the elastic wires 1.
In actual use of such a wire loop type instrument for an endoscope, the elastic wires 1 are axially moved back and forth to catch a polyp or other similar projection of tissue, and the polyp or the like caught in the loop is pinched tight with the elastic wires 1. Accordingly, the elastic wires 1 are repeatedly bent with a small radius of curvature at entrances A and B of the binding pipes 2 and 5 at the distal and proximal ends of the elastic wires 1.
Thus, the elastic wires 1 are inserted and fixed at both ends thereof in the respective binding pipes 2 and 5 and repeatedly bent at the borders between the fixed portions and the non-fixed portions thereof. Consequently, large stress concentration occurs at the bent portions of the elastic wires 1. Therefore, the elastic wires 1 are likely to break within a short period of time and readily develop a habit of bending undesirably.